Directly Laminated Plate

ABSTRACT

The invention relates to a directly laminated plate or board ( 1 ) that is produced by hot-pressing a core ( 3 ) with absorbent, resin-impregnated layers ( 4, 6 ), wherein at least one board surface has a decorative layer ( 4 ) with a graphic representation ( 5 ) of the surface of an imitated material, in addition to a resin-impregnated, transparent cover layer ( 6 ) on said decorative layer ( 4 ), with a relief-like reproduction of the surface structure ( 7 ) of the imitated material, where a resinous intermediate ply ( 10 ) is provided between the decorative layer ( 4 ) and the core ( 3 ).

The invention relates to a directly laminated plate or board that is produced by hot-pressing a core and absorbent, resin-impregnated layers, wherein at least one board surface has a decorative layer with a graphic representation of the surface of an imitated material, in addition to a resin-impregnated, transparent cover layer on said decorative layer, with a relief-like reproduction of the surface structure of the imitated material.

Imitated materials include, for example, building materials, such as wood, ceramics, natural stone and artificial stone. The artificial image of such a material can portray details, such as a material surface in the treated state, like painted wood, or in the worn state with signs of wear, etc. In the text below, the abbreviation “DPL”, which stands for “Direct Pressure Laminate”, is used to refer to directly laminated boards of this kind. DPL boards are manufactured in what is known as a cycle press, in which the individual layers are placed loosely on top of one another and positioned such that the graphic representation and the structured press plate are exactly in line on top of one another before pressing takes place. This is the unique feature of boards of the type presented here. An attempt is made to match the graphic representation to the tactile properties of the board, such that it is recognisable to the user. Upon close examination of the board, the palpable structure of the surface more or less corresponds to the graphic representation. With a wood decor, for example, the structure of a knot can be felt roughly at the point where the graphic representation of this knot is located on the layer below.

The boards are customarily made of a plate-like wood material core. Cores made of HDF (high-density fibreboard), MDF (medium-density fibreboard) or particle board are used.

Resin-impregnated decorative paper, fulfilling the function of graphic representation of the imitated material surface, is located on one surface of the core as the decorative layer. In contrast, imitation of the structure of the material surface of an original material is produced by means of another layer, namely a resin-impregnated overlay serving as the cover layer. A press plate with a negative of the required surface structure serves to impress the positive structure into the overlay during hot-pressing.

As a result of the process of hot-pressing in a DPL press, locally restricted areas of the overlay are provided with impressions that reach close up to the decorative paper. Projecting areas remain between the deep impressions in the overlay. A high surface pressure arises under the deeply impressed areas of the overlay during hot-pressing, whereas the areas adjacent to the impressed areas are subjected to less pressure.

The core of the board, e.g. an HDF core, displays a very hard and firm surface, on which the decorative paper is located. During hot-pressing, the decorative paper is strongly squeezed and compressed at the points where deep impressions are pressed into the overlay above. This effect impairs the optical impression offered by the graphic representation, as well as the homogeneity and stability of the decorative paper, since the pulp fibres are crushed.

The object of the invention is to design a directly laminated plate or board, which has a graphic representation of an imitated material corresponding to the relief-like reproduction of its surface, where the hot-pressing process has a gentle effect on the decorative layer.

According to the invention, the object is solved in that a resinous intermediate ply is provided between the decorative layer and the core.

The resinous intermediate ply is soft during hot-pressing and serves as a buffer into which the decorative paper is pressed. The decorative paper is no longer pressed on the hard surface of the core and crushed. In finished state, the decorative paper can be wavy. In this case, at the impressed points of the overlay, it dips somewhat deeper into the intermediate ply than at the points on either side of an impressed point. No crushing of the paper fibres occurs.

The intermediate ply can simply consist of a coating applied to the core prior to hot-pressing. This simplifies lamination of the board, since the absorbent core of the board, which usually consists of HDF, MDF or particle board material, is completely wetted. As a result, there is no danger of the dry core absorbing so much resin that the quantity remaining on the surface is insufficient for firm bonding.

The thickness of the resin coating of the intermediate ply is preferably in the range between zero and the thickness of the intermediate ply. This applies to both sides of the intermediate ply, where the layer thicknesses can be different.

A different alternative provides for the intermediate ply to be produced prior to hot-pressing, as a separate, prefabricated adhesive layer containing impregnating resin. This configuration offers advantages in terms of production engineering when large boards are to be manufactured. The adhesive layer can be impregnated by the same, known method as the overlay and decorative papers, whereas the coating of a core made of MDF, HDF or particle board is more complex as regards production engineering.

In order for the quantity of impregnating resin in the adhesive layer to be sufficient for bonding with the core, the adhesive layer contains excess resin. The excess amount is tailored to the absorbency of the respective core material. The less the core material is compressed, the higher the quantity of excess resin that must be selected. Therefore, a relatively large quantity of excess resin is required for a core material made of particle board, which absorbs a large amount of resin in its open-fibre structure during hot-pressing.

It is useful if the adhesive layer displays a matrix in which impregnating resin is embedded. Depending on the type of matrix, it can be provided with impregnating resin below its saturation point, or display an excess of impregnating resin that adheres to the surface of the saturated matrix. The matrix is favourably made of paper, because paper absorbs impregnating resin very well.

The decorative layer is preferably made of a cellulose material. Paper, in particular, can serve as the decorative layer, where the graphic representation of an imitated material is applied to the paper by means of a colour printing process, for example. One key aspect of the invention is that a quantity of impregnating resin, lying in the range from 0% to 100% of the absorbency of the cellulose material for hot, liquid resin, is applied to the cellulose material of the decorative layer prior to hot-pressing of the layers. According to the prior art, decorative paper is impregnated with excess resin. This means that the absorbent cellulose material reaches a degree of saturation equal to 100% of its absorbency, where an additional amount of impregnating resin is provided on at least one side of the layer. The latter is not embedded, but rather adheres to the cellulose material after being applied. The extensive saturation with hot, liquid resin causes the cellulose material to swell, this being manifested by the paper becoming longer and wider. According to the prior art, decorative papers that are impregnated are always used to manufacture directly laminated boards in which the graphic representation corresponds to the embossed surface structure.

The known decorative papers are provided with the graphic representation of the imitated material in a print shop. The print shop then delivers the decorative paper to a company that impregnates the printed paper with resin. Finally, the paper is delivered from there to the laminate manufacturer, who presses it into a board by the DPL method.

When applying the graphic representation, the printer absolutely must take into account the expected expansion of the cellulose material that is caused by impregnation with hot, liquid resin. In this context, the objective is, after the resin dries, to obtain a paper which, when it expands, corresponds to the size and pattern of the press plate of the DPL press, so that the graphic representation and the structure are not offset.

Because of the differing orientation of the cellulose fibres in the decorative paper, the lengthwise and widthwise expansion of the paper is not necessarily uniform. When printing the graphic representation, for example, it is assumed that the width increases by 1.6% and the length by 0.6%. Therefore, the print of the graphic representation is reduced in such a way that the paper, when expanded, reaches theoretical nominal dimensions corresponding to the dimensions of the press plate.

A number of factors are responsible for the expansion of the paper after impregnation, such as the quality of the cellulose, the processing method in the papermaking machine, the humidity during manufacture and storage, different dye liquors for printing the graphic representation, the quality of the impregnating resin, particularly its composition and the mixing ratio of water and hardener, the metering of the amount of impregnating resin in the impregnating machine, the additives used, such as fly ash, etc.

When processing the printing ink, there is seen to be a tendency for ink with low coverage, such as ink for printing a light-coloured maple wood surface, to promote expansion, while dark printing ink with greater coverage, such as for printing a dark mahogany wood surface, reduces expansion. This is because the more opaque ink seals the cellulose surface more strongly and the hot, liquid resin is therefore not able to penetrate the cellulose material so much from the printed paper side.

In view of the numerous factors governing paper expansion, it is understandable that the printer's reduction of the graphic representation can only ever be an approximation of the target dimensions required to match the dimensions of the paper in its expanded state to the size of the press plate.

To reduce the effect of paper expansion, the invention abandons the impregnation of the decorative layer with excess resin. Instead, the quantity of impregnating resin selected is in the range from 0% to 100% of the absorbency of the cellulose material. Since the objective is to reduce paper expansion, quantities of impregnating resin below 100%, i.e. below the saturation point, are preferably used. As a result, residual areas of the cellulose material remain dry, meaning that the paper expands less than paper impregnated with excess resin. Since the quality and structure of the paper, as well as the other factors mentioned above, also influence expansion, it is important to adapt the degree of resin impregnation of the decorative paper to the resin content of the layers above and beneath it. An overlay impregnated with resin is provided on top of the decorative layer as a cover layer, and a resinous intermediate ply is provided under the decorative layer. During hot-pressing, a sufficient amount of resin must be present at the boundary surfaces between the layers in order to bond them together tightly and permanently. For a low-quality paper, the degree of resin impregnation should be in the range from 0% to 20% of what the decorative layer is capable of absorbing. Impregnation with a quantity of impregnating resin in this range is used for papers that are expected to display relatively great expansion. The resin content is always adapted to the resin content of the intermediate ply beneath and the cover layer on top, since these layers form the reservoir for a sufficient quantity of resin for durable bonding of the layers.

A higher degree of resin impregnation in the decorative layer, namely in the range from 20% to 40% of the absorbency of the cellulose material, is provided for papers displaying less expansion, and is again adapted to the resin content of the intermediate ply and the cover layer, from which areas of the decorative paper that are still dry are supplied with hot, liquid resin during hot-pressing.

A higher degree of resin impregnation, e.g. in the range between 40% and 60% of the absorbency of the cellulose material, can be provided for papers with a lesser tendency to warping and expansion, such as papers made up of several layers with different fibre orientation. Once again, the resin content is adapted to the resin content of the intermediate ply and the cover layer. The latter require less excess resin because less resin has to pass from these layers into the dry areas of the cellulose material of the decorative layer during hot-pressing.

Degrees of resin impregnation in the range between 80% and 100% of the absorbency of the cellulose material can be provided for special decorative papers or materials demonstrating very little expansion due to moisture, in which case just a small amount of excess resin in the intermediate ply and the cover layer suffices to bring about complete and durable bonding of the layers.

A particularly important aspect of the present invention is the measure of using a decorative layer made of paper that is dry prior to hot-pressing and contains no impregnating resin whatsoever. This eliminates the effect of expansion due to the moisture of the hot, liquid resin. The paper need not be transported to an impregnating company, but rather can be delivered directly from the printer to the DPL press and processed into a laminated board. The problem of paper expansion in the making of the decorative layer is thus eliminated. The printer need no longer take resin-related expansion into account. The graphic representation of the imitated material can be printed directly in a size ratio of 1:1. The additional step of reducing the size of the graphic representation becomes superfluous.

The advantage of processing decorative layers with little or no expansion due to moisture is particularly important in the industrial-scale manufacture of directly laminated boards, because of the large dimensions of the presses used for laminating the layers. In the case of a very small press, e.g. with a length and width of one metre, and paper expansion of 1.6%, deviations from the target expansion value are small and tolerable. However, in the case of a relatively large press, paper expansion of 1.6% causes a significantly greater deviation from the target value. As a result, large sections of a directly laminated board become scrap. Errors of this kind are all the more costly, because only whole boards can usually be sent on for further processing.

For further processing, the directly laminated boards are, for example, sawn into a number of panels that are processed into wall, floor or ceiling coverings.

Apart from directly pressing the layers in a cycle press, joining layers in a continuous pressing process is another known method. In this case, the layers to be applied to the core are wound up and fed from rolls.

The solution according to the invention for avoiding paper expansion makes it possible to manufacture boards displaying a structured surface by a continuous pressing method, where the structure corresponds exactly to the graphic representation of an underlying decorative layer. In this context, the structure must be embossed by a roller in a rotary process. Even minimal paper expansion would be problematic in this process, because an error in lining up the graphic representation with the surface structure would persist as the process continues and worsen due to the continuous unwinding from the roll.

An example of the invention is illustrated in a drawing below and described in detail on the basis of the figures. The figures show the following:

FIG. 1: A cross-section of a section of a directly laminated board,

FIG. 2: A cross-section of a section of a directly laminated board according to the invention.

Board 1 shown in FIG. 1 is a board 1 according to the prior art. Decorative layer 4 is applied to top side 2 of core 3 made of HDF material (high-density fibreboard). Decorative layer 4 has a graphic representation 5 of an imitated material. Decorative layer 4 is provided with cover layer 6 comprising an overlay impregnated with resin. Surface structure 7, which simulates the surface of the imitated material, is embossed on the overlay. The objective is for graphic representation 5 of decorative layer 4 to be positioned exactly on top of embossed surface structure 7 of cover layer 6. In this way, the optical impression of graphic representation 5 is intended to match the tactile impression of embossed surface structure 7.

According to the prior art, decorative layer 4 is made of printed paper, which is also impregnated with resin prior to hot-pressing. The decorative paper lies directly on core 3 of the board. On underside 8 of the board, which faces away from decorative layer 4, core 3 is provided with backing 9, also referred to as the “balancing backing”. Backing 9 is likewise usually made of paper impregnated with resin. The thickness of the backing paper roughly corresponds to the sum of the thicknesses of decorative layer 4 and cover layer 6. Without backing 9, the laminated board would warp due to the different tensions in core 3 and the layer structure (4, 5) during cooling.

According to the prior art shown in FIG. 1, the embossing of cover layer 6 causes virtually identical compression of decorative paper 4, namely on its printed side.

The cellulose fibres in decorative paper 4 are crushed and damaged. The quality of graphic representation 5 on the previously flat printed surface of the decorative paper is impaired by the deformation.

The prior art is furthermore associated with the problem of lining up graphic representation 5 of an imitated material with embossed surface structure 7. In this context, it is not a true alignment problem, but rather a dimension problem, because the expansion of impregnated decorative paper differs from one sheet of paper to another.

If a directly laminated board is not provided with an additional resinous layer between decorative layer 4 and core 3, the decorative paper itself must be impregnated with resin. The decorative paper must be impregnated with resin because a certain amount of the resin serves as an adhesive between the decorative paper and core 3 during hot-pressing, in order to ensure a tight and permanent bond between the layers.

FIG. 2 shows a directly laminated board according to the invention, with a decorative layer 4 made of printed decorative paper. Graphic representation 5 on the decorative paper corresponds to surface structure 7 embossed on cover layer 6 positioned on top of decorative layer 4. The graphic representation of the image 5, and the roughness of surface structure 7 are imitations of a material surface, such as wood, ceramics, artificial stone, natural stone, etc.

In order to ensure gentle hot-pressing of decorative layer 4, a resinous intermediate ply 10 is provided between decorative layer 4 and core 3. In the present configuration, intermediate ply 10 is, prior to hot-pressing, a separate, prefabricated adhesive layer 10 that is impregnated with resin.

Adhesive layer 10 displays a matrix in which the impregnating resin is embedded. The matrix is likewise made of paper. The resin content of the paper corresponds to the saturation point of the paper plus excess resin, which adheres to the surfaces of the paper. With this structure, adhesive layer 10 forms a reservoir with a sufficient amount of resin to bond the paper to core 3. The HDF material of core 3 absorbs some of the excess resin. The same applies to the other side of adhesive layer 10, which is joined to decorative paper 4. It also forms a reservoir for the purpose of bonding the adhesive-layer paper to decorative paper 4.

Decorative paper 4 according to FIG. 2 is a dry paper with no impregnating resin, and it displays great absorbency for the resin of adhesive layer 10. The excess resin of adhesive layer 10 is tailored to the absorbency of core 3 and dry decorative paper 4, and it ensures a tight and permanent bond between layers 3, 4, 6 and 10.

It can be seen in FIG. 2 that structure 7, embossed on the surface of cover layer 6, causes considerably less deformation on the printed side of decorative paper 4 than is the case with the prior art, shown in FIG. 1, because adhesive layer 10, located underneath decorative paper 4, is soft and flexible. At the deeply impressed points of cover layer 6, decorative paper 4 can dip down into adhesive layer 10 without being crushed against the hard surface of core 3. As a result, the hot-pressing process is gentle on decorative paper 4. The stability of decorative paper 4 and the quality of graphic representation 5 are preserved.

Using non-impregnated decorative paper 4, in accordance with the invention, eliminates the problem of applying to decorative paper 4 a colour print that has reduced dimensions and does not approximately reach the dimensions of the associated press plate until it expands.

To manufacture the directly laminated board according to the invention, a decorative paper 4 is used whose dimensions correspond 1:1 to the surface of an imitated material, without any size reduction. It exactly matches the dimensions of the corresponding press plate of a DPL press. All factors influencing the expansion of impregnated paper, as named above in the description of the invention, are thus eliminated. As a result, the invention simplifies the manufacture of such directly laminated boards, in which a graphic representation 5 is aligned with a surface structure 7.

On underside 8 of core 3, the side opposite the decorative layer, the board shown in FIG. 2 also has a backing 9 made of paper impregnated with resin, the thickness of which roughly corresponds to the total thickness of layers 4, 6 and 10 on the top side of core 3, in order to balance the tension forces on both sides of core 3 that occur during cooling of a freshly pressed board.

LIST OF REFERENCE NUMBERS Directly Laminated Plate

-   1 Plate or board -   2 Top side -   3 Core -   4 Decorative layer/decorative paper -   5 Graphic representation -   6 Cover layer -   7 Surface structure -   8 Underside -   9 Backing -   10 Intermediate ply/adhesive layer 

1. Directly laminated plate or board (1) that is produced by hot-pressing a core (3) with absorbent, resin-impregnated layers (4, 6), wherein at least one board surface has a decorative layer (4) with a graphic representation (5) of the surface of an imitated material, in addition to a resin-impregnated, transparent cover layer (6) on said decorative layer (4), with a relief-like reproduction of the surface structure (7) of the imitated material, characterised in that a resinous intermediate ply (10) is provided between the decorative layer (4) and the core (3).
 2. Directly laminated plate or board according to claim 1, characterised in that the intermediate ply (10) is formed by a resin coating applied to the core (3) prior to hot-pressing.
 3. Directly laminated plate or board according to claim 2, characterised in that the thickness of the resin coating is . . . [state sensible thickness range].
 4. Directly laminated plate or board according to claim 1, characterised in that the intermediate ply (10) is produced prior to hot-pressing, as a separate, prefabricated adhesive layer (10 a) with impregnating resin.
 5. Directly laminated plate or board according to claim 4, characterised in that the impregnation of the adhesive layer (10 a) contains excess resin.
 6. Directly laminated plate or board according to claim 4 or 5, characterised in that the adhesive layer (10 a) displays a matrix in which impregnating resin is embedded.
 7. Directly laminated plate or board according to claim 6, characterised in that the matrix is made of paper.
 8. Directly laminated plate or board according to one of claims 1 to 7, characterised in that the decorative layer (4) is made of a cellulose material, particularly paper, which displays a quantity of impregnating resin in the range from 0% to 100% of the absorbency of the cellulose material.
 10. Directly laminated plate or board according to claim 9, characterised in that the degree of resin impregnation is in the range from 0% to 20% of the absorbency of the cellulose material, and is adapted to the resin content of the intermediate ply (10) and the cover layer (6).
 11. Directly laminated plate or board according to claim 9, characterised in that the degree of resin impregnation is in the range from 20% to 40% of the absorbency of the cellulose material, and is adapted to the resin content of the intermediate ply (10) and the cover layer (6).
 12. Directly laminated plate or board according to claim 9, characterised in that the degree of resin impregnation is in the range from 40% to 60% of the absorbency of the cellulose material, and is adapted to the resin content of the intermediate ply (10) and the cover layer (6).
 13. Directly laminated plate or board according to claim 9, characterised in that the degree of resin impregnation is in the range from 60% to 80% of the absorbency of the cellulose material, and is adapted to the resin content of the intermediate ply (10) and the cover layer (6).
 14. Directly laminated plate or board according to claim 9, characterised in that the degree of resin impregnation is in the range from 80% to 100% of the absorbency of the cellulose material, and is adapted to the resin content of the intermediate ply (10) and the cover layer (6).
 15. Directly laminated plate or board according to claim 9, characterised in that the decorative layer (4) is made of a paper without resin impregnation that is dry prior to hot-pressing. 